Why the register that controls sub-clock oscillator lie in two places?

Question:

Why does the register that controls operation/stopping of the sub-clock oscillator exist in two places?

Answer:

Please use the appropriate register according to whether the sub-clock is used as a system clock or a real-time clock.
- When using as a system clock, set the sub-clock oscillator stop bit (SOSCCR.SOSTP) to 0 (sub-clock oscillator is operating).
- When using as a count source for a real-time clock, set the sub-clock oscillator control bit (RCR3.RTCEN) to 1 (permitting input from the sub-clock oscillator).
- When not using as either a system clock or a real-time clock, set the SOSCCR.SOSTP bit to 1 (sub-clock oscillator is stopped) and the RCR3.RTCEN bit to 0 (sub-clock oscillator is stopped).